Anyone interested in commenting to me privately, good or bad, can send email to sciencesprings@gmail.com

Google+

Sciencesprings has restarted at Google+. Please add sciencesprings to your Google+ circles. Just go to Google+ and search for "sciencesprings." What will come up is Richard Mitnick. That's O.K.,that's it, take it.

Event recorded with the CMS detector in 2012 at a proton-proton centre of mass energy of 8 TeV. The event shows characteristics expected from the decay of the SM Higgs boson to a pair of photons (dashed yellow lines and green towers). Image: L. Taylor, CMS collaboration /CERN

The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

CERN ATLAS

CDERN CMS

But more precise studies of it are needed than the LHC is able to provide. That is why, years earlier, a machine like the International Linear Collider had been envisioned as a Higgs factory, and the Higgs discovery set the stage for its possible construction.

ILC schematic

Over the years, instruments for probing the universe have become more sophisticated. More refined data has hinted that aspects of the Standard Model are incomplete. If built, a machine such as the ILC will help reveal how wide a gulf there is between the universe and our understanding of it by probing the Higgs to unprecedented levels. And perhaps, as some physicists think, it will uproot the Standard Model and make way for an entirely new physics.

In the textbook version, the Higgs boson is a single particle, and its alleged progenitor, the mysterious Higgs field that pervades every point in the universe, is a single field. But this theory is still to be tested.

“We don’t know whether the Higgs field is one field or many fields,” said Michael Peskin of SLAC’s Theoretical Physics Group. “We’re just now scratching the surface at the LHC.”

The LHC collides proton beams together, and the collision environment is not a clean one. Protons are made up of quarks and gluons, and in an LHC collision it’s really these many component parts – not the larger proton – that interact. During a collision, there are simply too many components in the mix to determine the initial energies of each one. Without knowing them, it’s not possible to precisely calculate properties of the particles generated from the collision. Furthermore, Higgs events at the LHC are exceptionally rare, and there is so much background that the amount of data that scientists have to sift through to glean information on the Higgs is astronomical.

“There are many ways to produce an event that looks like the Higgs at the LHC,” Peskin said. “Lots of other things happen that look exactly like what you’re trying to find.”

The ILC, on the other hand, would collide electrons and positrons, which are themselves fundamental particles. They have no component parts. Scientists would know their precise initial energy states and there will be significantly fewer distractions from the measurement standpoint. The ILC is designed to be able to accelerate particle beams up to energies of 250 billion electronvolts, extendable eventually to 500 billion electronvolts. The higher the particles’ energies, the larger will be the number of Higgs events. It’s the best possible scenario to probe the Higgs.

If the ILC is built, physicists will first want to test whether the Higgs particle discovered at the LHC indeed has the properties predicted by the Standard Model. To do this, they plan to study Higgs couplings with known subatomic particles. The higher a particle’s mass, the proportionally stronger its coupling ought to be with the Higgs boson. The ILC will be sensitive enough to detect and accurately measure Higgs couplings with light particles, for instance with charm quarks. Such a coupling can be detected at the LHC in principle but is very difficult to measure accurately.

The ILC can also help measure the exact lifetime of the Higgs boson. The more particles the Higgs couples to, the faster it decays and disappears. A difference between the measured lifetime and the projected lifetime—calculated from the Standard Model—could reveal what fraction of possible particles—or the Higgs’ interactions with them— we’ve actually discovered.

“Maybe the Higgs interacts with something new that is very hard to detect at a hadron collider, for example if it cannot be observed directly, like neutrinos,” speculated John Campbell of Fermilab’s Theoretical Physics Department.

These investigations could yield some surprises. Unexpected vagaries in measurement could point to yet undiscovered particles, which in turn would indicate that the Standard Model is incomplete. The Standard Model also has predictions for the coupling between two Higgs bosons, and physicists hope to study this as well to check if there are indeed multiple kinds of Higgs particles.

“It could be that the Higgs boson is only a part of the story, and it has explained what’s happened at colliders so far,” Campbell said. “The self-coupling of the Higgs is there in the Standard Model to make it self-consistent. If not the Higgs, then some other thing has to play that role that self-couplings play in the model. Other explanations could also provide dark matter candidates, but it’s all speculation at this point.”

The Standard Model has been very self-consistent so far, but some physicists think it isn’t entirely valid. It ignores the universe’s
accelerating expansion caused by dark energy, as well as the mysterious dark matter that still allows matter to clump together and galaxies to form. There is speculation about the existence of undiscovered mediator particles that might be exchanged between dark matter and the Higgs field. The Higgs particle could be a likely gateway to this unknown physics.

With the LHC set to be operational again next year, an optimistic possibility is that a new particle or two might be dredged out from trillions of collision events in the near future. If built, the ILC would be able to build on such discoveries, just as in case of the Higgs boson, and provide a platform for more precise investigation.

The collaboration between a hadron collider like the LHC and an electron-positron collider of the scale of the ILC could uncover new territories to be explored and help map them with precision, making particle physics that much richer.

Some 2000 scientists – particle physicists, accelerator physicists, engineers – are involved in the ILC or in CLIC, and often in both projects. They work on state-of-the-art detector technologies, new acceleration techniques, the civil engineering aspect of building a straight tunnel of at least 30 kilometres in length, a reliable cost estimate and many more aspects that projects of this scale require. The Linear Collider Collaboration ensures that synergies between the two friendly competitors are used to the maximum.

In September 2013, the Science Council of Japan (SCJ) published a report on the ILC. This report contains two key statements and requests.

Concerning the scientific justification for the ILC:

“The Committee appreciates that the ILC enables the precision measurements of the detailed properties of the Higgs particle and the top quark, thereby exploring the physics beyond the Standard Model of particle physics and, therefore, it acknowledges that the ILC is endowed with the scientific value in particle physics. The Committee, however, expresses the desire for more compelling and articulate argument to justify the ILC project in order to search for unknown particles and the physics beyond the Standard Model, running concurrently with the upgraded LHC, given the considerable investment it will require.”

The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

Concerning the project cost:

“Before making the final decision of whether the ILC should be hosted in Japan, the issues and concerns described in this document should be fully investigated and a clear vision for solutions needs to be provided. They include the whole profile of project cost for the construction, operation, upgrades and decommissioning, as well as prospect for cost-sharing among the countries involved. Also included are the issues related to human resources and management/operation organization.”

In response, the Ministry of Education, Sports, Science and Technology (MEXT) set up a “Task force for ILC” under the vice-Minister, which itself set up an “Academic Experts Committee” which first met in May 2014. At that meeting the committee formed two working groups in order to respond to the two key requests of the SCJ.

In order to address the scientific issues a “Particle and Nuclear Physics Working Group” led by Takaaki Kajita (Director of the Institute for Cosmic Ray Research, University of Tokyo) was formed. The timetable and subjects for meetings of this Working Group as known so far is as follows:

24 June 2014: Status of Particle Physics and ILC physics overview.

29 July 2014: Future prospects in the US and Europe

27 August 2014: Cosmic ray and Astrophysics and ILC.

22 September 2014: Flavour and neutrino physics and ILC

21 October 2014: Interim summary to be reported to Experts Committee.

In order to address technical issues, a “Technical Design Report Validation” Working Group has been formed under the leadership of Hideaki Yokomizo (Former Trustee of JAEA). The first open meeting of this working group was held on 30 June 2014, giving an overview. Further working group meetings are in progress for detailed discussions on the TDR contents with cost-estimates in closed sessions.

Information is being fed to this working group through the ILC Planning Office at KEK after verification by the LCC. Note that at the present time, this is a purely internal Japanese process. All committee and working group members are Japanese and no input is requested from outside Japan except indirectly through the LCC so far.

In addition to setting up this Committee and its Working Groups, on 19 August MEXT published a Call for Tender for a survey:

“Research, survey and analysis on technology spinoffs and subsequent economic ripple effects expected from the International Linear Collider (ILC) project and the global trend of the particle/nuclear physics research including technology R&D.”

This survey will be conducted by a private company, yet to be chosen, and should be completed by the end of March 2015. It is expected that this company will consult with the major laboratories world-wide.

I hope that the upcoming LCWS14 workshop in Belgrade will help refine the scientific arguments and differentiate the International Linear Collider from the other proposed lepton colliders and help our Japanese colleagues to feed correct and compelling arguments to the working groups.

Some 2000 scientists – particle physicists, accelerator physicists, engineers – are involved in the ILC or in CLIC, and often in both projects. They work on state-of-the-art detector technologies, new acceleration techniques, the civil engineering aspect of building a straight tunnel of at least 30 kilometres in length, a reliable cost estimate and many more aspects that projects of this scale require. The Linear Collider Collaboration ensures that synergies between the two friendly competitors are used to the maximum.

Last month, LC NewsLine reported the achievement of the world’s smallest beam size of 55 nanometres at the ATF2 facility at KEK. At two international conferences held in June and July, the next record of 44 nanometres was reported by Kiyoshi Kubo and Shigeru Kuroda.

The beam line at ATF2 is designed as a prototype of the final focus system of the ILC, with basically the same optics, similar beam energy spread, natural chromaticity and tolerances of magnetic field errors.

ILC schematic

For linear colliders, realising an extremely small and stable beam is essential. At the ILC, the design vertical beam size and required position stability at the interaction point is at the nanometer level. The target beam size at ATF is 37 nanometres. Because of the difference in the beam energy, 37 nanometres at ATF will correspond to smaller than 5 nanometres at the ILC, the specification for the ILC design.. The result presented at ICHEP and IPAC was just one step away from the target size.

Kubo said the most important factor of the improvement was the stabilisation of the beam orbit by improving the feedback system. “We installed a new magnet for better feedback and improved the software, which worked to stabilise the beam. The beam was stable for 30 to 60 minutes without tuning in most cases.”

“Also, we removed as much possible strong wakefield sources on every weekend when we stop the operation,” said Kuroda. “To put it in a nutshell, the further stabilisation of the beam and reduction of wakefield,” said Kuroda about the contributing factors.

The beam size is still slightly larger than the target size of 37 nanometres. ATF is now under summer shut-down, and the scientists are planning to work on the remaining issues in the autumn this year.

Some 2000 scientists – particle physicists, accelerator physicists, engineers – are involved in the ILC or in CLIC, and often in both projects. They work on state-of-the-art detector technologies, new acceleration techniques, the civil engineering aspect of building a straight tunnel of at least 30 kilometres in length, a reliable cost estimate and many more aspects that projects of this scale require. The Linear Collider Collaboration ensures that synergies between the two friendly competitors are used to the maximum.

The component, called the final focus optics, will help produce precise beams of particles at these future research facilities, said Glen White, the SLAC accelerator physicist who is lead author on a recent paper in Physical Review Letters.

Optics for an accelerator that boosts charged particles to near light speed aren’t lenses in the typical sense of eyeglass lenses or magnifying lenses. Instead, “optics” refers to the magnets that steer the particles. The final focus optics for an accelerator are a sequence of powerful magnets that concentrate particles into tight beams. The optics demonstrated by the Accelerator Test Facility 2 (ATF2) focused an electron beam down to only a few tens of nanometers tall.

This special sequence of magnets was developed by former SLAC accelerator physicists Andrei Seryi and Pantaleo Raimondi nearly 15 years ago. Many more SLAC physicists are members of the ATF2 collaboration, an international group of scientists that built and continue to test the structure at the KEK accelerator facility in Japan.

The optics for a future linear collider must take many different issues into account, said White, including the physics and the economics of extremely energetic beams of tiny particles.

For example, a magnet will focus charged particles that have slightly different energies to slightly different places.”No bunch of particles in an accelerator is perfectly uniform,” said White. Thus, the particles can “fuzz out” around the focal point, resulting in fewer collisions and less data, unless such differences in position, called chromatic aberrations, are accounted for.

Previous methods for correcting chromatic aberration, such as those tested during the Final Focus Test Beam experiment at SLAC, required additional lengthy sections of tunnel for the magnets used, thus adding considerable cost, White said. The design the ATF2 collaboration tested involved adding magnets called sextupoles to the focusing magnets, called quadrupoles, already in use. “The sextupoles refocus the particles according to their positions, which are determined by their energies,” he said – essentially reversing the errors introduced by the quadrupoles.

Sextupole electromagnet as used within the storage ring of the Australian Synchrotron to focus and steer the electron beam

A quadrupole electromagnet as used in the storage ring of the Australian Synchrotron

Seryi, who left SLAC in 2010 to become director of the John Adams Institute for Accelerator Science at Oxford University, is a member of the ATF2 collaboration. “It is extremely gratifying to see the idea realized in practice and know that it works,” he said. “I am also tremendously happy that the ATF2 experiment has trained many young accelerator physics experts. This was actually one of the goals – to create the team who will be able to work on the linear collider’s final focus when the real project starts.”

Now that they know it works, said White, the next steps are to work on stabilizing the beam and train more young physicists for the real thing.

SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.

“The Compact Linear Collider and International Linear Collider will accelerate particles and create collisions in different ways. Nonetheless, the detector concepts under development share many commonalities.

ILC Top, CLIC Bottom

CERN physicist Dominik Dannheim explains that CLIC detector plans are adaptations of the ILC detector designs with a few select modifications. ‘When we started several years ago, we did not want to reinvent the wheel,’ says Dannheim. The approved ILC detector concepts served as an excellent starting point for our designs.’

Essential differences

Both CLIC and ILC scientists foresee general-purpose detectors that make measurements with exquisite precision. These colliders, however, have very different operating parameters, which will have important consequences for the various detector components. The ILC’s collision energy is set at 500 GeV (with option to upgrade to 1 TeV), while CLIC will collide at up to 3 TeV. And the bunch structure is very different, too. The main difference is in the timing of the collisions. At the ILC electrons and positrons collide in bunch crossings spread out over bunch trains of almost a millisecond. At CLIC these bunch trains last for only 156 nanoseconds. So CLIC detectors will have a tougher job disentangling the rare physics events from the collision background.

The higher energy will give CLIC a greater physics reach, but will also create more unwanted background events with less time to disentangle background from more interesting phenomena. “Simulations have shown that a time resolution at the nanosecond level is needed for most sub-detectors at CLIC,” says Dannheim. “In this respect they will be similar to the ones currently in operation at the LHC, yet aiming for much higher granularity and measurement precision.”

Vertex detector

The detector component closest to the interaction point, where collisions occur, is the vertex detector. ILC concepts place a paper-thin pixel detector near the interaction point to improve the resolution of short-lived particles created in collisions.

The harsher background conditions at CLIC required a redesign of the inner detectors, which included moving the vertex detector further away from the interaction point. CLIC scientists are developing a different type of pixel detector for this region, where thin sensors are coupled to dedicated ultra-fast low-power readout chips (called CLICpix). This technology will help limit the number of overlapping background particles that inevitably blur the result. First prototypes of the newly developed CLICpix readout chip and of 50-μm-thin sensors have recently been produced, marking important milestones for the CLIC vertex detector project. The ultra-thin sensors will be under scrutiny in the DESY test beam telescope in the next two weeks.”

While the Large Hadron Collider at CERN is producing exciting results like the discovery of a new particle that could be the Higgs boson, scientists around the world are already planning the next big collider to take the discoveries to the next level. Even though there is no decision yet which collider will be built or where, there is consensus in the scientific community that the results from the LHC will have to be complemented by a collider that can study the discoveries in greater detail by producing different kinds of collisions.

The Linear Collider Collaboration is an organisation that brings the two most likely candidates, the Compact Linear Collider Study (CLIC) and the International Liner Collider (ILC), together under one roof. Headed by former LHC Project Manager Lyn Evans, it strives to coordinate the research and development work that is being done for accelerators and detectors around the world and to take the project linear collider to the next step: a decision that it will be built, and where.

Some 2000 scientists — particle physicists, accelerator physicists, engineers — are involved in the ILC or in CLIC, and often in both projects. They work on state-of-the-art detector technologies, new acceleration techniques, the civil engineering aspect of building a straight tunnel of at least 30 kilometres in length, a reliable cost estimate and many more aspects that projects of this scale require. The Linear Collider Collaboration ensures that synergies between the two friendly competitors are used to the maximum.